INFLUENCING THE APPROACH TO THE LOCALIZATION THRESHOLD

We argue that the Thouless criterion for localization is universal. Because the Thouless number delta is the ratio of the width and spacing of the modes of the sample, it can be adjusted by changing the macroscopic characteristics of the sample, such as the transverse dimensions, the reflectivity at the boundaries and the character of internal microstructure resonances. We find the dependence of the correlation parameter delta-1 and hence of the proximity to the localization threshold upon these characteristics. These results are illustrated by microwave and optical experiments.